Cold protection of tropical fruit trees in the Florida landscape for homeowners

Scott Walker

Introduction
Hurricanes, droughts and pests are among the biggest problems affecting tropical fruit growers in Florida, but one of the most problematic factors in Florida is a freeze.
Since the turn of the century, citrus growers have used various methods to protect crops from impending freezes including the use of smudge pots, tenting and flooding. The original Temple orange tree was saved from a destructive freeze in 1917 when its owner, Louis Hakes, stayed up all night "babysitting" the treasured tree. He used a kerosene heater and a large tent over the tree, in which he camped out on a cot through the night. Talk about dedication.
In 1989 Florida suffered a major freeze when temperatures fell into the teens in Central Florida and lower 30’s in even the southernmost areas of the state. This event destroyed many citrus groves as well as tropical fruit trees - both commercial and residential. Even over the past few years there have been drops in temperature during the winter months which prompted many to take protective measures to preserve their crops and trees.

Types of freezes
Freezes can be classified as either radiational or advective. A radiational freeze occurs when a cold air mass settles into an area. During this type of freeze, there is little to no wind and cloud cover is absent. However when cloud cover is present, it acts as a greenhouse effect, trapping in ground heat as it is released throughout the night. Some wind can also be beneficial, as it does not allow cold air to settle in any one area.
Advective freezes are characterized by windy conditions accompanied by a large dry air mass rapidly moving into an area. This creates a sudden and rapid drop in temperature and makes it difficult to protect sensitive plants. Wind breaks may help in this situation, but saving the trunk and graft union may be the best focus of attention.

The Basics of cold protection
One of the primary methods of protecting fruit trees from cold weather is location of planting. The south and southeast sides of a home are typically the most warm, absorbing heat from the sun throughout the day and releasing some of that heat during the night. Many growers water the ground copiously the day prior to a freeze as the wet ground absorbs more heat from the sun and slowly releases it throughout the night. This in combination with covering a small tree can be enough to prevent damage to a tree that would otherwise suffer. Another method is covering small trees to prevent heat loss and frost. Some of the materials used for covering are burlap, sheets, frostcloth or blankets. Plastic is not recommended unless a frame is built around the tree so the plastic is not touching the plant, as this can lead to foliar damage.
An additional factor in determining survival in trees is the health of the tree itself. A well nourished tree will cope with stress and cold far better than an unhealthy tree. A regular nutrition program consisting of either organic or chemical fertilizer will bring the tree into the winter months with an advantage. It is important however to end feeding by October to prevent growth flushes which would be susceptible to cold weather.

Even colder
For more severe freezes a combination of covering and lights can be used. The standard C-7 or C-9 Christmas lights offer a great source of heat that does not harm the plants or create a fire hazard when used according to label instructions. Others methods of heat are standard light bulbs and portable flood lights. It is important when using a high wattage electrical heat source, such as a flood lamp, that all precautions are used according to labels and directions so as not to cause a fire.
When trees become so large that covering is no longer practical, lights may be used in combination with wrapping the trunk and major structural branches with blankets or cardboard. Using this method, even if foliage or small limbs are damaged, the tree itself should recover.

After the Freeze
The morning after a freeze, when the temperature rises above 32 degrees, plants should be uncovered. Initial damage may not be visible and may not show for a few weeks. One reason to refrain from pruning is that some branches may look damaged but will actually recover. In addition, pruning may initiate a premature growth flush that could be damaged by another cold event. Transpiration (water loss through the leaves) is a problem that can occur on a sunny day after a freeze. Plants should be monitored for water needs and water may be applied to both thaw the soil and provide moisture.

Other options
If the threat of cold is a factor due to location (i.e., living in a cold pocket or in the northernmost parts of the state), subtropical fruits are good alternate choices. Fruits such as blueberries, jujubes, pomegranates, Oriental persimmons and white sapote are excellent hardy additions to a landscape. There are also cultivars of avocado such as Brogdon, Lula, Gainesville, Winter Mexican and Choquette that will survive temperatures from the low to mid 20’s.

Summary

· Two types of freezes - Advective and Radiational
· Planting location – South side of house is best
· Nourish trees in early Fall
· Soak the ground (under the trees) with water the day prior to a predicted freeze
· Cover plants /trees with – frostcloth, burlap, sheets or blankets. Large cardboard boxes (refrigerator) can also be used for smaller trees
· Wrap trunk (from branching to ground level) with blankets or other material for extra protection
· On coldest nights Christmas lights (C-9 or C-7) add heat
· After freeze - Remove covers, watch for desiccation and hold off on pruning
· In a consistently cold area consider subtropical fruit trees

Cold Sensitivity of Tropical and Sub Tropical fruits in Florida
Fruit Scientific name *Average cold tolerance of adult trees (in Fahrenheit)
Avocado Persea Americana 25-30
Ambarella (Dwarf) Spondias dulcis 28
Atemoya Annona cherimola x squamosa 28
Banana Musa spp. 29
Barbados cherry Malpighia punicifolia 29
Black Sapote Diospyros digyna 29
Blackberry Robus argatus 20
Blackberry jam fruit Randia formosa 29
Blueberry** Vaccinium corymbosum (blossom) 28
Canistel Pouteria campechiana 28
Carambola Averrhoa carambola 28
Ceriman Monstera deliciosa 31
Cherry of the Rio Grande Eugenia aggregata 25
Fig** Ficus carica 15
Green Sapote Pouteria viridis 27
Grumichama Eugenia braziliensis 28
Guava Psidium guajava 27
Jaboticaba Myrciaria cauliflora 26
Jackfruit Artocarpus heterophyllus 29
Jujube** Ziziphus jujuba 26
Longan Nephelium longana 26
Loquat** Eriobotrya japonica 22
Lychee Litchi chinensis 28
Mamey Sapote Poiteria sapota 29
Mango Mangifera indica 28
Miracle fruit Synsepalum dulcificum 29
Mombin Spondias purpurea 28
Papaya Carica papaya 30
Passion fruit Passiflora edulis 30
Peanut butter fruit Bunchosia argenta 30
Persimmon (Oriental)** Diospyros kaki L. 15
Pineapple Ananas comosus 29
Pitaya Hylocereus sp. 28
Pitomba Eugenia luschnathiana 28
Pomegranate** Punica granatum 24
Rollinia Rollinia deliciosa 29
Rose apple Syzygium jambos 27
Sapodilla Manilkara zapota 28
Strawberry tree Muntingia calabura 28
Sugar apple Annona squamosa 28
Tamarind Tamarindus indica 28
White sapote** Casimiroa edulis 25

** Subtropical or Temperate

Again, with temps less than than 32f and young trees, heat AND cover is recommended. If there is one thing I have learned is that things will recover (even if only a small bit above the graft line survives) and within a year can make a remarkable recovery.

Bluepalm, thanks! I think I have seen pics of your yard and trees..very nice selection!

Gatormom, I can't stress enough that pruning should wait until March 15 (and even at that date check the forecast). If nothing else the dead brown ugly branches and leaves may act as a buffer for the live growth. I try and follow the natural regrowth patterns of a tree or plant and this regrowth after freeze damage usually occurs around March.
No pruning!

Thank you for posting this very invaluable info on the fruit trees. Just like everybody else, I am too worried about my so prized fruit trees.

But since I went through this the last year, I took some precautions this year. The very sensitive are in pots either in the garage or porch. The other ones I hope they will make it.

Last year I lost a mango and a star fruit, the Brogdon is still alive and so is the atemoya. Papayas I can afford to loose, they are cheap enough from seed and grow fast too.

Good luck to us all after this cold snap!

Silvia

Since I really tend to push the limit on tropical fruits and my location is 9a, I have to use something that really works. I am a big fan of what you call "tenting" with plastic. I make a framework, so to speak, of tall green garden stakes around the tree. Then, I often cover the top of the tree with a sheet and then wrap the whole tree in plastic securing it with twine and clothespins. I have found the 20' x 25' sheets to be the best size for medium sized trees.

As for a heat source, I prefer to use the large bulb Christmas lights. But, I have a 2 acre yard so I have to resort to using hurricane lamps filled with kerosene, one to two lamps per tree.

Here are some pictures taken last year. This is a young Key lime and avocado:

Now, I really took on a challenge by planting a mango. Last year it was a very small tree but with the help of "tenting" with heat, it has grown quite a bit during the year. This picture is from last year:

This is a picture that I took to prove that this method of protection works. The mango flowers are untouched by the freeze. Notice the damage to the banana plants in the background:

Christine --- vice-president of The Tropical Fruit Club

Kate

Christine, great photos! The mango tenting clearly worked well and the contrast with the bananas is amazing. Great job!
This year I tried a framing method that I learned from Richard Campbell of Fairchild - it is inexpensive and breaks down easily for storage.
Materials used are:
4 10' x 3/4" sections of PVC ($.77 each)
1 Four way connector (cross) 3/4" PVC coupler
4 18" pieces of rebar
4 bolts or cotter pins.

Basically you create a domed frame by assembling each section of PVC pipe into the cross coupler (at this point I drilled small holes through the coupler and the inserted PVC and slid in a small bolt to make sure the PVC didn't pop out of the coupler) and then driving 4 rebar sections into the ground around the tree (vertically). The assembled PVC unit is then bent and inserted onto the 4 rebar pieces creating a dome frame that can then be covered with plastic or cloth.
It sounds more complicated than it really is and if I could figure out how to post pics I would!

Scott

Carol

All of the "saunas" (PVC frame, light source and cover) I put up around trees were at least 5-7 degrees warmer than surrounding areas, and that's with just bedsheets. I think the agribon is probably warmer, and plastic might even hold in more heat. (next year)

My yard today looks mushy (ornamentals) but the covered 4' Lychees and small Mangos are looking fine. My lowest reading was 23.7 last night and I'm sure we were below freezing at least 12 hours.

This is not pleasant but it is very interesting feedback and good for the journal...ha ha

Bluepalm, I had those handwarmers out all night under a small Fairchild mango, a small Rosigold and a Pink Ohia Lychee and was very surprised that they did not show that much damage. This may be a great thing! I'll try them again tonight and thanks for the re-shaking advice.
When my wife (God bless her) unwrapped the trees this morning at 9:30 they were still warm!

Good luck to all, this by far (barring cloud cover or wind) will be the coldest night yet.

Scott

Scott, would love a photo of your PVC frame or maybe Carol can post one...when you get yours built. Thanks again!

Additionally, the PVC sections can be cut to match the height of each tree as needed. A full 10' frame can enclose an 8' tree.

What did you do with the big blue tub of water? And to be more nosy, what's in the 5-gallon pail (and what did you do with it)?!

Well the buckets are kind of an experiment/advice from an old grower. Basically it takes thermal energy to both heat water and freeze water. I have found that the buckets of water seem to regulate temps inside frames that have no source of heat (in areas of the yard w/out power). Pepper growers have used this method, I think they called it infared heating. Not sure what the results will be with temps this low but it's worth a shot!

greenhouser2, this year seems to be an exception to the norm, especially in an El Nino year that is supposed to suppress these Arctic plunges. Have no fear!

G.houser, I agree Sarasota doesn't usually get this type of weather...its pretty rare. I lived in Bradenton just north,lived there for 12 years and only remember a few nights in that time frame where we had freeze.

Last season I lost a Persian Lime , Myers Lemon and Dancy Tangerine this way .
The lime branches and leaves fried immediately but not the trunk; that died later .
The lemon and a few orange trees had peeling bark 6 to 8 months after last year's deep freeze .
This round might just do 'em in for good .

No , I did not protect those trees .
I have protected a young Lee Tangerine year after year and it is still chugging along . Will it make it again ?
Only time will tell - time meaning months and years .
Temper your celebration of survival with the knowledge that trees can show damage long long after the initial injury .

The hand warmer packet idea is also good especially since I already have some in my closet that I forgot about.

I thought that I might have the northern most planted Key lime tree. Without protection I know that mine would be dead.

Can't wait for winter to be over!

Christine

This year the mango tree is 8 feet tall and doing well under the plastic with heat for the last week and a half. If tonight is really the last freeze for a while, I get to take the plastic off tomorrow.

Christine

Scott, you did a great job on this article. I enjoyed reading it and learned a lot.

I'm particularly interested in the cold frames you made with the PVC. Last year I made some out of wood for my mom and stapled plastic to it. I will not do that again.

I have a few questions for you, if you don't mind.

(1) What width or diameter PVC did you use? I didn't realize PVC was that flexible. What makes it hold that shape?

(2) Did you just sink the ends of the PVC directly into the ground? I couldn't tell because of the blankets.

I'd like to be prepared long before winter sets in this winter. Your frames are great because they look easy to construct and easy to dismantle & store when not in use.

Thank you.

I'm glad you found the information interesting. I'm happy to say that in the worst winter I have experienced ever in Vero, all of the trees that were covered and lit using this method are not only alive but blooming and flourishing. It works.

To answer your questions:

1. 3/4" PVC (the cheapest @ $.77 for a 10ft section)

2. The PVC is slid over rebar (2' sections) that are driven into the ground.

They bend easily (and straighten back out easily), and the bending is just from the tension of one end in the 4way connector and the other in the rebar base.

Hope this helps!

Scott

I'm so glad to hear that all of your trees that were protected by this method are blooming and thriving. It sure makes it worth the effort when they survive.

Great job!

http://www.amazon.com/Emergency-Thermal-Blankets-4-Pack/dp/B0007N0XDO